Air-conditioning apparatus

ABSTRACT

Providing an air-conditioning apparatus that is capable of securing safety while reducing load to the environment. 
     The air-conditioning apparatus  100  includes a concentration detection device  305  that detects the concentration of a heat source side refrigerant leaking from the refrigerant circuit, shut off devices (first shut off device  303  and second shut off device  304 ) that shut off the circulation of the heat source side refrigerant on the basis of information from the concentration detection device  305.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus which is applied to, for example, a multi-air-conditioning apparatus for a building.

BACKGROUND ART

In conventional air-conditioning apparatuses such as a multi-air-conditioning apparatus for a building, a refrigerant is circulated between an outdoor unit, which is a heat source unit disposed, for example, outside a building, and indoor units disposed in rooms in the building. The refrigerant transfers heat or removes heat to heat or cool air, thus heating or cooling a conditioned space through the heated or cooled air. In such a multi-air-conditioning apparatus for a building, a plurality of indoor units is connected, and there are many cases in which indoor units not in operation and indoor units in operation co-exist. Further, there are cases in which the piping connecting the outdoor unit and the indoor units extend up to a length of 100 meters at the most. The longer the piping, the greater the refrigerant amount charged into the system will become.

Indoor units of these multi-air-conditioning apparatuses for a building are typically disposed and used in indoor spaces where people exist (office spaces, habitable rooms, and stores, for example). If, by any cause, the refrigerant were to leak from an indoor unit disposed in an indoor space, depending on the type of refrigerant in which some has inflammability and toxicity, a grave problem from the viewpoint of effect to the human body and safety will be created. Further, even if the refrigerant is not toxic to the human body, cases can be assumed in which the oxygen content of air in the indoor space decrease due to the leakage of the refrigerant, and, accordingly, causing adverse effects to the human body. Hence, a technique is disclosed in which a system is suspended when there is a leakage of refrigerant from the refrigeration cycle (see, for example, Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2000-320936 (Page 5 and other pages, for example)

SUMMARY OF INVENTION Technical Problem

Incidentally, in recent years, from the view point of global warming, there has been a trend in restricting the use of HFC based refrigerants that has high global warming potential (for example, R410, R404A, R407C, R134a, and the like), and an air-conditioning apparatus using refrigerants that has low global warming potential (for example, carbon dioxide and the like) has been proposed. Measures when the refrigerant leak into the indoor space need to be taken even when using carbon dioxide as a refrigerant for an multi-air-conditioning apparatus for a building, because a large amount of refrigerant is to be used.

Referring to Table 1, practical limit in a case of leakage of a conventional refrigerant (R410A) and carbon dioxide are shown. The table indicates that when under the practical limit (kg/m³) of Table 1, there will be no adverse effect to the human body. These values are from the values in ISO 5149. As can be understood from Table 1, the practical limit of carbon dioxide is substantially small compared to the practical limit of the conventional refrigerant. That is, compared to the conventional refrigerant, carbon dioxide requires only a small amount of refrigerant leakage to cause adverse effect to the human body.

TABLE 1 PRACTICAL LIMIT OF REFRIGERANTS Refrigerant Practical Limit (kg/m³) R410A 0.44 Carbon Dioxide 0.07

In the technique described in Patent Literature 1, carbon dioxide is used as the refrigerant and when there is a leakage of carbon dioxide refrigerant in the same manner of leakage as that of the conventional refrigerant, the system is suspended. However, Patent Literature 1 does not implement any measures against the leakage of carbon dioxide. That is, when using carbon dioxide as a refrigerant, a major premise should be such that no adverse effect will be caused to the human body, and thus, a measure of some kind to reduce the leakage of refrigerant needs to be implemented.

The invention has been made to solve the above problem and provides an air-conditioning apparatus capable of reducing environmental load while securing safety.

Solution to Problem

The air-conditioning apparatus according to the present invention includes an indoor unit including at least an expansion device and a use side heat exchanger; a refrigerant circuit being formed by refrigerant piping connecting the compressor, the heat source side heat exchanger, the expansion device, and the use side heat exchanger, in which a heat source side refrigerant that transmits to a supercritical state circulates; a concentration detection device detecting a concentration of the refrigerant that has leaked from the refrigerant circuit, the concentration detection device provided in the indoor unit or in the installation space of the indoor unit; and a shut off device that shuts off the circulation of the heat source side refrigerant on the basis of information from the concentration detection device, the shut off device provided inside the indoor unit on outlet and inlet sides.

The air-conditioning apparatus according to the present invention includes an outdoor unit including at least a compressor and a heat source side heat exchanger; a heat medium relay unit including at least a heat exchanger related to heat medium, expansion device, and a pump; an indoor unit including at least a use side heat exchanger; a refrigerant circuit being formed by refrigerant piping serially connecting the compressor, the heat source side heat exchanger, the expansion device, and a refrigerant side passage of the heat exchanger related to heat medium, in which a heat source side refrigerant that transmits to a supercritical state circulates; a heat medium circuit being formed by piping serially connecting a heat medium passage of the heat exchanger related to heat medium, the pump, and the use side heat exchanger, in which a heat medium circulates; concentration detection device detecting a concentration of the refrigerant that has leaked from the refrigerant circuit, the concentration detection device provided in the heat medium relay unit or in the installation space of the heat medium relay unit; and a shut off device that shuts off the circulation of the heat source side refrigerant on the basis of information from the concentration detection device, the shut off device provided inside the heat medium relay unit on outlet and inlet sides.

Advantageous Effects of Invention

The air-conditioning apparatus according to the invention enables detection of refrigerant leakage from the refrigerant circuit and is capable of substantially increasing safety as well as reducing environmental load.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic circuit diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 1 of the invention.

FIG. 2 is a refrigerant circuit diagram illustrating a flow of a refrigerant in a cooling operation mode of the air-conditioning apparatus according to Embodiment 1 of the invention.

FIG. 3 is a refrigerant circuit diagram illustrating a flow of the refrigerant in a heating operation mode of the air-conditioning apparatus according to Embodiment 1 of the invention.

FIG. 4 is a schematic diagram schematically illustrating an exemplary internal configuration of an indoor unit.

FIG. 5 is a schematic diagram schematically illustrating another exemplary internal configuration of the indoor unit.

FIG. 6 is a schematic diagram illustrating an exemplary installation of an air-conditioning apparatus according to Embodiment 2 of the invention.

FIG. 7 is a schematic circuit diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus according to Embodiment 2 of the invention.

FIG. 8 is a refrigerant circuit diagram illustrating flows of refrigerants in a cooling only operation mode of the air-conditioning apparatus according to Embodiment 2 of the invention.

FIG. 9 is a refrigerant circuit diagram illustrating flows of refrigerants in a heating only operation mode of the air-conditioning apparatus according to Embodiment 2 of the invention.

FIG. 10 is a refrigerant circuit diagram illustrating flows of refrigerants in a cooling main operation mode of the air-conditioning apparatus according to Embodiment 2 of the invention.

FIG. 11 is a refrigerant circuit diagram illustrating flows of refrigerants in a heating main operation mode of the air-conditioning apparatus according to Embodiment 2 of the invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will be described below with reference to the drawings.

Embodiment 1

FIG. 1 is a schematic circuit diagram illustrating an exemplary circuit configuration of an air-conditioning apparatus 100 according to Embodiment 1 of the invention. The detailed circuit configuration of the air-conditioning apparatus 100 will be described with reference to FIG. 1. FIG. 1 illustrates an example in which four indoor units 300 are connected. It should be noted that the dimensional relationships of components in FIG. 1 and other subsequent figures may be different from the actual ones.

As illustrated in FIG. 1, the air-conditioning apparatus 100 includes an outdoor unit (heat source unit) 200 and indoor units 300 (indoor unit 300 a to 300 d) connected by pipings 400 (piping 400 a and 400 b). Specifically, in the air-conditioning apparatus 100, a plurality of indoor units 300 are connected in parallel with the outdoor unit 200. Note that the pipings 400 are refrigerant pipings that communicate a refrigerant (heat source side refrigerant). Further, it is assumed that the air-conditioning apparatus 100 is filled with carbon dioxide (CO₂) as its refrigerant. However, the refrigerant is not limited to carbon dioxide, and other single mixed refrigerants, mixed refrigerants (such as a mixed refrigerant of carbon dioxide and diethyl ether), or the like that transmits to a supercritical state may be used.

Outdoor Unit 200

The outdoor unit 200 includes a compressor 201, an oil separator 202, a refrigerant flow switching device 203, such as a four-way valve, a heat source side heat exchanger 204, and an accumulator 205, which are connected in series with the refrigerant pipings 400. Further, the oil separator 202 and the suction side of the compressor 201 are connected with an oil return capillary 206.

The compressor 201 sucks in the heat source side refrigerant, compress the heat source side refrigerant to a high-temperature high-pressure state, and conveys the refrigerant to the refrigerant circuit. The compressor 201 may include, for example, a capacity-controllable inverter compressor. The oil separator 202 is provided on the discharge side of the compressor 201 and separates the refrigerant and a refrigerating machine oil. The flow switching device 203 is provided downstream of the oil separator 202 and switches between a refrigerant flow during a heating operation mode and a refrigerant flow during a cooling operation mode.

The heat source side heat exchanger (outdoor side heat exchanger) 204 functions as an evaporator during heating operation and functions as a radiator (gas cooler) during cooling operation, and exchanges heat between air supplied by an air-sending device (not shown), such as a fan, and the refrigerant. The accumulator 205 is provided on the suction side of the compressor 10 and retains excessive refrigerant caused by a difference in the heating operation mode and the cooling operation mode and excessive refrigerant caused by a transitional operation change (change in the number of operating indoor units 300, for example). The oil return capillary 206 returns the refrigerating machine oil captured by the oil separator 202 to the low-pressure side of the compressor 201.

Indoor Units 300

In each indoor unit 300, a first shut off device 303, an expansion device 302, a use side heat exchanger (indoor side heat exchanger) 301, and a second shut off device 304 are mounted in series. Each first shut off device 303 includes, for example, a two-way valve and is configured to open or close the piping 400 a. Each first shut off device 303 is provided on a piping 400 a side of a corresponding use side heat exchanger 301. Each use side heat exchanger 301 functions as a radiator during the heating operation and functions as an evaporator during the cooling operation, and exchanges heat between the air supplied by an air-sending device (not shown), such as a fan, and the refrigerant to generate air for heating or air for cooling that is supplied to a conditioned space.

Each expansion device 302 has a function of a reducing valve and an expansion valve and decompresses and expands the refrigerant. Each expansion device 302 may include a component having a variably controllable opening degree, such as an electronic expansion valve. Each second shut off device 304 includes, for example, a two-way valve and are configured to open or close the refrigerant piping 400 b. Each second shut off device 304 is provided in a piping 400 a between the expansion device 302 a and the heat source side heat exchanger 204.

Embodiment 1 shows a case in which four indoor units 300 are connected. Illustrated are, from the bottom of the drawing, an indoor unit 300 a, an indoor unit 300 b, an indoor unit 300 c, and an indoor unit 300 d. In addition, the use side heat exchangers 301 are illustrated as, from the bottom of the drawing, a use side heat exchanger 301 a, a use side heat exchanger 301 b, a use side heat exchanger 301 c, and a use side heat exchanger 301 d corresponding to the indoor units 300 a to 300 d respectively. Similarly, the expansion devices 302 are illustrated as, from the bottom of the drawing, an expansion device 302 a, an expansion device 302 b, an expansion device 302 c, and an expansion device 302 d.

Similarly, the first shut off devices 303 are illustrated as, from the bottom of the drawing, a first shut off device 303 a, a first shut off device 303 b, a first shut off device 303 c, and a first shut off device 303 d. Similarly, the second shut off devices 304 are illustrated as, from the bottom of the drawing, a first shut off device 304 a, a first shut off device 304 b, a first shut off device 304 c, and a first shut off device 304 d. Note that the connected number of indoor units 300 is not limited to four.

Various operation modes executed by the air-conditioning apparatus 100 will be described below.

Cooling Operation Mode

FIG. 2 is a refrigerant circuit diagram illustrating a flow of the refrigerant in a cooling operation mode of the air-conditioning apparatus 100. In FIG. 2, an exemplary case in which all of the indoor units 300 are driven will be described. Note that in FIG. 2, arrows indicate the flow direction of the refrigerant.

A low-temperature low-pressure refrigerant is compressed by the compressor 201 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant that has been discharged from the compressor 201 flows into the oil separator 202. In the oil separator 202, the refrigerant and the refrigerating machine oil that is mixed in the refrigerant are separated. The separated refrigerating machine oil passes through the oil return capillary 206 and returns to the low-pressure side of the compressor 201, and eventually returns to the compressor 201. The high-temperature high-pressure gas refrigerant that has been separated in the oil separator 202 flows through the flow switching device 203 into the heat source side heat exchanger 204.

The high-temperature high-pressure gas refrigerant that has flowed into the heat source side heat exchanger 204 exchanges heat with the air supplied from the air-sending device (not shown) and, thus, transfers heat to the air. Since carbon dioxide is used as the refrigerant, the high-temperature high-pressure gas refrigerant that has flowed into the heat source side heat exchanger 204 flows out of the heat source side heat exchanger 204 in a supercritical state with its temperature reduced. This low-temperature high-pressure refrigerant in a supercritical state flows out of the outdoor unit 200 through the piping 400 a, and then flows into each of the indoor units 300 a to 300 d.

The refrigerant that has flowed into the indoor units 300 a to 300 d, passes through the first shut off devices 303 a to 303 d, is expanded (decompressed) in each of the expansion devices 302 a to 302 d, and turns into a low-temperature low-pressure two-phase gas-liquid state. This two-phase gas-liquid refrigerant flows into each of the use side heat exchangers 301 a to 301 d. The two-phase gas-liquid refrigerant that has flowed into the use side heat exchangers 301 a to 301 d exchanges heat with the air (indoor air) supplied from the air-sending device (not shown) to remove heat from the air, turns into a low-pressure gas refrigerant, and flows out of the use side heat exchangers 301 a to 301 d.

Temperature sensors (a temperature sensor 306 and a temperature sensor 307 shown in FIG. 4) are typically provided in the refrigerant inlets and outlets of each use side heat exchanger 301. Further, the refrigerant amount supplied to each use side heat exchanger 301 is controlled by using temperature information from each temperature sensor provided in the refrigerant inlet and outlet of each use side heat exchanger 301. Specifically, the refrigerant amount supplied to each use side heat exchanger 301 is controlled by, based on the information from the corresponding temperature sensors, calculating the degree of superheat (a refrigerant temperature on the outlet side—a refrigerant temperature on the inlet side) and by determining the opening degree of the corresponding expansion device 302 so that the degree of superheat is around 2 to 5 degrees C.

The low-pressure gas refrigerant that has flowed out of the use side heat exchangers 301 a to 301 d flows out of the indoor units 300 a to 300 d through the second shut off devices 304 a to 304 d, passes through the piping 400 b, and flows into the outdoor unit 200. The refrigerant that has flowed into the outdoor unit 200 flows into the accumulator 205 through the flow switching device 203. The refrigerant that has flowed into the accumulator 205 is separated into a liquid refrigerant and a gas refrigerant, of which the gas refrigerant is sucked into the compressor 201 again.

In the above cooling operation, since the degree of superheat in each indoor unit 300 is controlled, the refrigerant in a liquid state does not flow into the accumulator 205. However, during transitional operation or when there is a suspended indoor unit 300, there are cases in which a small amount of refrigerant in a liquid state (approximately 0.95 of quality) flows into the accumulator 205. The liquid refrigerant that has flowed into the accumulator 205 evaporates and is sucked into the compressor 201, or is sucked into the compressor 201 through the oil return hole (not shown) provided in the outlet piping of the accumulator 205.

Heating Operation Mode

FIG. 3 is a refrigerant circuit diagram illustrating a flow of the refrigerant in a heating operation mode of the air-conditioning apparatus 100. In FIG. 3, an exemplary case in which all of the indoor units 300 are driven will be described. Note that in FIG. 3, arrows indicate the flow direction of the refrigerant.

A low-temperature low-pressure refrigerant is compressed by the compressor 201 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant that has been discharged from the compressor 201 flows into the oil separator 202. In the oil separator 202, the refrigerant and the refrigerating machine oil that is mixed in the refrigerant are separated. The separated refrigerating machine oil passes through the oil return capillary 206 and returns to the low-pressure side of the compressor 201, and eventually returns to the compressor 201. The high-temperature high-pressure refrigerant that has been separated in the oil separator 202 passes through the piping 400 b via the flow switching device 203 and flows out of the outdoor unit 200. The refrigerant that has flowed out of the outdoor unit 200 flows into each of the indoor units 300 a to 300 d.

The high-temperature high-pressure gas refrigerant that has flowed into the indoor units 300 a to 300 d passes through the second shut off devices 304 a to 304 d, exchanges heat with the air (indoor air) supplied from the air-sending device (not shown) in the use side heat exchangers 301 a to 301 d to transfer heat to the air, and flows out of the use side heat exchangers 301 a to 301 d in a supercritical state with its temperature reduced. This low-temperature high-pressure refrigerant in a supercritical state is expanded (decompressed) in each of the expansion devices 302 a to 302 d, turns into a low-temperature low-pressure two-phase gas-liquid state, passes through the first shut off devices 303 a to 303 d, and flows out of the indoor units 300 a to 300 d.

Typically, in the refrigerant outlet of each use side heat exchanger 301, a temperature sensor, as described above, and a pressure sensor (a pressure sensor 308 shown in FIG. 4) are provided. Further, the refrigerant amount supplied to each use side heat exchanger 301 is controlled by using information from each temperature sensor and pressure sensor provided in the refrigerant outlet of each use side heat exchanger 301. Specifically, the refrigerant amount supplied to each use side heat exchanger 301 is controlled by, based on the information from the corresponding sensors, calculating the degree of subcooling (a saturation temperature converted from a detection pressure of the refrigerant on the outlet side—a refrigerant temperature on the outlet side) and by determining the opening degree of the corresponding expansion device 302 so that the degree of subcooling is around 2 to 5 degrees C.

The low-temperature low-pressure two-phase gas-liquid refrigerant that has flowed out of the indoor units 300 a to 300 d flows into the outdoor unit 200 through the piping 400 a. This refrigerant flows into the heat source side heat exchanger 204. The low-temperature low-pressure two-phase gas-liquid refrigerant that has flowed into the heat source side heat exchanger 204 exchanges heat with the air supplied from the air-sending device (not shown), receives heat from the air, and gradually increases its quality. Further, the refrigerant turns into a two-phase gas-liquid refrigerant with high quality at the outlet of the heat source side heat exchanger 204 and flows out of the heat source side heat exchanger 204. The refrigerant that has flowed out of the heat source side heat exchanger 204 flows through the flow switching device 203 and into the accumulator 205. The refrigerant that has flowed into the accumulator 205 is separated into a liquid refrigerant and a gas refrigerant, of which the gas refrigerant is sucked into the compressor 201 again.

In the above heating operation, excessive refrigerant exists in the accumulator 205 at all times. The liquid refrigerant that has flowed into the accumulator 205 evaporates and is sucked into the compressor 201 or is sucked into the compressor 201 through the oil return hole (not shown) provided in the outlet piping of the accumulator 205.

FIG. 4 is a schematic diagram schematically illustrating an exemplary internal configuration of the indoor unit 300. FIG. 5 is a schematic diagram schematically illustrating another exemplary internal configuration of the indoor unit 300. Features of the air-conditioning apparatus 100 according to Embodiment 1 will be described with reference to FIGS. 4 and 5. As described above, each indoor unit 300 is provided with the first shut off device 303, the expansion device 302, the use side heat exchanger 301, and the second shut off device 304. Further, as shown in FIGS. 4 and 5, each indoor unit 300 is provided with the temperature sensor 306, the temperature sensor 307, the pressure sensor 308, and a concentration detection device 305.

Each temperature sensor 306 is provided between the corresponding first shut off device 303 and use side heat exchanger 301 and detects the temperature of the refrigerant flowing through this portion. Each temperature sensor 307 is provided between the expansion device 302 and the use side heat exchanger 301 and detects the temperature of the refrigerant flowing through this portion. Each pressure sensor 308 is provided in a similar position as that of the corresponding temperature sensor 307 and detects the pressure of the refrigerant flowing through this portion. Each concentration detection device 305 detects the concentration of the refrigerant (in Embodiment 1, carbon dioxide), and in particular, detects the refrigerant concentration in a space where people exist.

Note that although in FIGS. 4 and 5, an exemplary case is shown in which the concentration detection device 305 is provided in the vicinity of the use side heat exchanger 301 in the indoor unit 300, the installing position is not limited to this position. For example, the concentration detection device 305 may be provided in the space in which the indoor unit 300 is disposed, rather than in the indoor unit 300. That is, since the aim of disposing the concentration detection device 305 is to detect the refrigerant concentration in the space where people exist, the concentration detection device 305 may be disposed in any position in the space where the indoor unit 300 is disposed. Further, the concentration detection device 305 may be incorporated in a remote control (not shown), for example.

In FIG. 4, an exemplary case is shown in which the first shut off device 303 is provided on the piping 400 a side of the use side heat exchanger 301 and the second shut off device 304 is provided on the piping 400 b side of the use side heat exchanger 301, and in which the expansion device 302 and the use side heat exchanger 301 are provided between the first shut off device 303 and the second shut off device 304. On the other hand, as shown in FIG. 5, the first shut off device 303 may be provided between the use side heat exchanger 301 and the expansion device 302. Further, the first shut off device 303 and the second shut off device 304 are in an opened state when energized and are in a closed state when in a non-energized state.

The concentration detection device 305 is built-in with a switch structure that is in a switch ON state when the concentration is under a predetermined level and is in a switch OFF state when the concentration is higher or equal to a predetermined level. Needless to say, a switch (contact) may be constituted as a separate part without the switch structure being built-in into the concentration detection device 305. This predetermined concentration is the practical limit of leakage of the refrigerant used. Since the practical limit of leakage of carbon dioxide used as a refrigerant is 0.07 (kg/m³) (see Table 1), the ON/OFF of the switch built-in in the concentration detection device 305 is normally carried out with this concentration as the predetermined concentration.

However, in consideration of the inconsistency of each of the concentration detection devices 305, the concentration distribution in the indoor space, and the like, in the air-conditioning apparatus 100, one tenth of the practical limit of leakage is set as the predetermined concentration. That is, in the air-conditioning apparatus 100, the switch is turned ON/OFF with the threshold value (predetermined concentration) of 0.007 (kg/m³). Specifically, when under 0.007 (kg/m³), the switch is in the ON state; and when more than or equal to 0.007 (kg/m³), the switch is in the OFF state.

Further, the electric components of the first shut off device 303 and the second shut off device 304 are not AC driven but DC driven. Since during normal operation of the air-conditioning apparatus 100, the first shut off device 303 and the second shut off device 304 are in an opened state, in order to respond to the demand of extending life of electrical components, DC driven first shut off device 303 and second shut off device 304 are employed rather than AC driven ones. Specifically, the opening and closing of the valves of each first shut off device 303 and second shut off device 304 are carried out by a stepping motor. That is, the first shut off device 303 and second shut off device 304 each include a stepping motor as its electrical component.

Further, since each first shut off device 303 is disposed on the high-pressure side (during the cooling operation), the CV value may be small such that CV=about 2 (1 or more) at about 5 HP (horse power). On the other hand, since each second shut off device 304 is disposed on the low-pressure side (during cooling operation), the CV value needs to be large such that CV=about 5 (5 or more) at about 5 HP. Note that, as shown in FIG. 5, when the first shut off device 303 is provided between the expansion device 302 and the use side heat exchanger 301, since it is in a low-pressure state during cooling operation, the first shut off device 303 needs to be selected with a large CV value. In this case, one with V=5 may be selected. However, by disposing the first shut off device 303 as shown in FIG. 4, the CV value thereof can be smaller, and, thus, is more advantageous in terms of cost.

Further, because a shut off device is inherently demanded to shut off in case of emergency, the minimum operating pressure differential of each first shut off device 303 and second shut off device 304 needs to be sufficiently small at about 0 (kPa). Furthermore, since the air-conditioning apparatus 100 is a heat pump air-conditioning apparatus that can switch between cooling and heating and, thus, since the flow is reversed, a first shut off device 303 and second shut off device 304 that is capable of passing the refrigerant in both directions are employed. Additionally, assuming cases of a blackout or failure of electric power supply from a commercial power supply to the concentration detection device 305, by using a built-in battery type concentration detection device 305, safety can be further increased.

In Embodiment 1, since carbon dioxide is used as the refrigerant, the amount of leakage from the first shut off device 303 and the second shut off device 304 needs to be small at about 3.0×10⁻⁹ (m²/sec). This amount is based on the assumption that carbon dioxide continues to leak for a few years in the smallest room in which the indoor unit 300 will be installed.

Next, the operation of the first shut off device 303 and the second shut off device 304 will be described. When the predetermined concentration of carbon dioxide of 0.007 (kg/m³) is detected by the concentration detection device 305, the controller (not shown) determines that refrigerant leakage has occurred, switches the concentration detection device 305 OFF, and stops energizing the first shut off device 303 and the second shut off device 304. As a result, the first shut off device 303 and the second shut off device 304 are turned into a closed state, and the refrigerant flowing from the outdoor unit 200 through the piping 400 a and 400 b can be shut off, and, thus, refrigerant leakage into the indoor space can be prevented.

The air-conditioning apparatus 100 that employs the above-described configuration is capable of detecting refrigerant leakage from the refrigerant circuit and is one with substantially improved safety. Further, since the air-conditioning apparatus 100 uses a refrigerant that transmits to a supercritical state, environmental load can be made small.

Embodiment 2

FIG. 6 is a schematic diagram illustrating an exemplary installation of an air-conditioning apparatus according to Embodiment 2 of the invention. The exemplary installation of the air-conditioning apparatus will be described with reference to FIG. 6. This air-conditioning apparatus uses refrigeration cycles (a refrigerant circuit A and a heat medium circuit B) in which refrigerants (a heat source side refrigerant or a heat medium) circulate such that a cooling mode or a heating mode can be freely selected as its operation mode in each indoor unit. Note that in Embodiment 2, portions different to that of Embodiment 1 will be mainly described and same parts as Embodiment 1 will be referred to with the same reference numerals and description thereof will be omitted.

In the air-conditioning apparatus 100 according to Embodiment 1, a method in which refrigerant is used directly (direct expansion method) is employed. However, in an air-conditioning apparatus according to Embodiment 2, a method in which refrigerant is used indirectly (indirect method) is employed. That is, the air-conditioning apparatus according to Embodiment 2 transfers cooling energy or heating energy stored in the heat source side refrigerant to a different refrigerant (hereinafter, referred to as a “heat medium”) and a conditioned space is cooled or heated with the cooling energy or heating energy stored in the heat medium.

Referring to FIG. 6, the air-conditioning apparatus according to Embodiment 2 includes a single outdoor unit 1, functioning as a heat source unit, a plurality of indoor units 2, and a heat medium relay unit 3 disposed between the outdoor unit 1 and the indoor units 2. The heat medium relay unit 3 exchanges heat between the heat source side refrigerant and the heat medium. The outdoor unit 1 and the heat medium relay unit 3 are connected with refrigerant pipings 4 thorough which the heat source side refrigerant flows. The heat medium relay unit 3 and each indoor unit 2 are connected with pipings 5 (heat medium pipings) through which the heat medium flows. Cooling energy or heating energy generated in the outdoor unit 1 is delivered through the heat medium relay unit 3 to the indoor units 2.

The outdoor unit 1 is typically disposed in an outdoor space 6 which is a space (e.g., a roof) outside a structure 9, such as a building, and is configured to supply cooling energy or heating energy through the heat medium relay unit 3 to the indoor units 2. Each indoor unit 2 is disposed at a position that can supply cooling air or heating air to an indoor space 7, which is a space (e.g., a living room) inside the structure 9, and supplies air for cooling or air for heating to the indoor space 7 that is a conditioned space. The heat medium relay unit 3 is configured with a housing separate from the outdoor unit 1 and the indoor units 2 such that the heat medium relay unit 3 can be disposed at a position different from those of the outdoor space 6 and the indoor space 7, and is connected to the outdoor unit 1 through the refrigerant pipings 4 and is connected to the indoor units 2 through the pipings 5 to convey cooling energy or heating energy, supplied from the outdoor unit 1 to the indoor units 2.

As illustrated in FIG. 6, in the air-conditioning apparatus according to Embodiment 2, the outdoor unit 1 is connected to the heat medium relay unit 3 using two refrigerant pipings 4, and the heat medium relay unit 3 is connected to each indoor unit 2 using two pipings 5. As described above, in the air-conditioning apparatus according to Embodiment 2, each of the units (the outdoor unit 1, the indoor units 2, and the heat medium relay unit 3) is connected using two pipings (the refrigerant pipings 4 or the pipings 5), thus construction is facilitated.

Furthermore, FIG. 6 illustrates an exemplary state in which each heat medium relay unit 3 is disposed in the structure 9 but in a space different from the indoor space 7, for example, a space above a ceiling (for example, a space above a ceiling in the structure 9, hereinafter, simply referred to as a “space 8”). The heat medium relay unit 3 can be disposed in other spaces, such as a common space where an elevator or the like is installed. In addition, although FIG. 6 illustrates a case in which the indoor units 2 are of a ceiling-mounted cassette type, the indoor units are not limited to this type and, for example, a ceiling-concealed type, a ceiling-suspended type, or any type of indoor unit may be used as long as the units can blow out heating air or cooling air into the indoor space 7 directly or through a duct or the like.

FIG. 6 illustrates a case in which the outdoor unit 1 is disposed in the outdoor space 6. The arrangement is not limited to this case. For example, the outdoor unit 1 may be disposed in an enclosed space, for example, a machine room with a ventilation opening, may be disposed inside the structure 9 as long as waste heat can be exhausted through an exhaust duct to the outside of the structure 9, or may be disposed inside the structure 9 when the used outdoor unit 1 is of a water-cooled type. Even when the outdoor unit 1 is disposed in such a place, no problem in particular will occur.

Furthermore, the heat medium relay unit 3 can be disposed near the outdoor unit 1. It should be noted that when the distance from the heat medium relay unit 3 to the indoor unit 2 is excessively long, because power for conveying the heat medium is significantly large, the advantageous effect of energy saving is reduced. Additionally, the numbers of connected outdoor units 1, indoor units 2, and heat medium relay units 3 are not limited to those illustrated in FIG. 6. The numbers thereof can be determined in accordance with the structure 9 where the air-conditioning apparatus according to Embodiment is installed.

FIG. 7 is a schematic circuit diagram illustrating an exemplary circuit configuration of the air-conditioning apparatus (hereinafter, referred to as an “air-conditioning apparatus 101”) according to Embodiment 2. The detailed configuration of the air-conditioning apparatus 101 will be described with reference to FIG. 7. As illustrated in FIG. 7, the outdoor unit 1 and the heat medium relay unit 3 are connected with the refrigerant pipings 4 through heat exchangers related to heat medium 15 a and 15 b included in the heat medium relay unit 3. Furthermore, the heat medium relay unit 3 and the indoor units 2 are connected with the pipings 5 through the heat exchangers related to heat medium 15 a and 15 b. Note that the refrigerant piping 4 will be described in detail later.

Outdoor Unit 1

The outdoor unit 1 includes a compressor 10, a first refrigerant flow switching device 11, such as a four-way valve, a heat source side heat exchanger 12, and an accumulator 19, which are connected in series with the refrigerant pipings 4.

The compressor 10 sucks in the heat source side refrigerant and compress the heat source side refrigerant to a high-temperature high-pressure state. The compressor 10 may include, for example, a capacity-controllable inverter compressor. The first refrigerant flow switching device 11 switches the flow of the heat source side refrigerant between a heating operation mode (heating only operation mode and heating main operation mode) and a cooling operation mode (cooling only operation mode and cooling main operation mode).

The heat source side heat exchanger 12 functions as an evaporator during heating operation and functions as a radiator (gas cooler) during cooling operation, and exchanges heat between the air supplied from an air-sending device (not shown), such as a fan, and the heat source side refrigerant. The accumulator 19 is provided on the suction side of the compressor 10 and retains excessive refrigerant caused by a difference in the heating operation mode and the cooling operation mode and excessive refrigerant caused by a transitional operation change (change in the number of operating indoor units 2, for example).

Indoor Units 2

The indoor units 2 each include a use side heat exchanger 26. The use side heat exchanger 26 is connected to a heat medium flow control device 25 and a second heat medium flow switching device 23 in the heat medium relay unit 3 with the pipings 5. Each of the use side heat exchangers 26 exchanges heat between air supplied from an air-moving device, such as a fan, (not illustrated) and the heat medium in order to produce air for heating or air for cooling supplied to the indoor space 7.

FIG. 7 illustrates a case in which four indoor units 2 are connected to the heat medium relay unit 3. Illustrated are, from the bottom of the drawing, an indoor unit 2 a, an indoor unit 2 b, an indoor unit 2 c, and an indoor unit 2 d. In addition, the use side heat exchangers 26 are illustrated as, from the bottom of the drawing, a use side heat exchanger 26 a, a use side heat exchanger 26 b, a use side heat exchanger 26 c, and a use side heat exchanger 26 d each corresponding to the indoor units 2 a to 2 d. As is the case of FIG. 6, the number of connected indoor units 2 illustrated in FIG. 7 is not limited to four.

Heat Medium Relay Unit 3

The heat medium relay unit 3 includes the two heat exchangers related to heat medium 15, two expansion devices 16, a single on-off device 17, four second refrigerant flow switching devices 18, two pumps 21, four first heat medium flow switching devices 22, the four second heat medium flow switching devices 23, the four heat medium flow control devices 25, a first shut off device 37, a second shut off device 38, and a concentration detection device 39. The first shut off device 37 and the second shut off device 38 are disposed on the inlet side and the outlet side of the heat medium relay unit 3, respectively.

Each of the two heat exchangers related to heat medium 15 (the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b) functions as a condenser (radiator) or an evaporator and exchanges heat between the heat source side refrigerant and the heat medium in order to transfer cooling energy or heating energy, generated in the outdoor unit 1 and stored in the heat source side refrigerant, to the heat medium. The heat exchanger related to heat medium 15 a is disposed between an expansion device 16 a, and a second refrigerant flow switching device 18 a(1) and a second refrigerant flow switching device 18 a(2) in the refrigerant circuit A and is used to cool the heat medium in a cooling and heating mixed operation mode. The heat exchanger related to heat medium 15 b is disposed between an expansion device 16 b, and a second refrigerant flow switching device 18 b(1) and a second refrigerant flow switching device 18 b(2) in the refrigerant circuit A and is used to heat the heat medium in the cooling and heating mixed operation mode.

The two expansion devices 16 (the expansion device 16 a and the expansion device 16 b) each have functions of a reducing valve and an expansion valve and are configured to reduce the pressure of and expand the heat source side refrigerant. The expansion device 16 a is disposed upstream of the heat exchanger related to heat medium 15 a, upstream regarding the heat source side refrigerant flow during the cooling only operation mode. The expansion device 16 b is disposed upstream of the heat exchanger related to heat medium 15 b, upstream regarding the heat source side refrigerant flow during the cooling only operation mode. Each of the two expansion devices 16 may include a component having a variably controllable opening degree, such as an electronic expansion valve.

The on-off device 17 (a third refrigerant flow switching device) includes, for example, a two-way valve and are configured to open or close the refrigerant piping 4. The on-off device 17 is provided in the refrigerant piping 4 between the first shut off device 37 and the heat exchanger related to heat medium 15 a.

The four second refrigerant flow switching devices 18 (the second refrigerant flow switching device 18 a(1), the second refrigerant flow switching device 18 a(2), the second refrigerant flow switching device 18 b(1), and the second refrigerant flow switching device 18 b(2)) each include, for example, a two-way valve and switch passages of the heat source side refrigerant in accordance with the operation mode. The second refrigerant flow switching devices 18 a (the second refrigerant flow switching device 18 a(1) and the second refrigerant flow switching device 18 a(2)) are disposed downstream of the heat exchanger related to heat medium 15 a, downstream regarding the heat source side refrigerant flow during the cooling only operation mode.

The second refrigerant flow switching devices 18 b (the second refrigerant flow switching device 18 b(1) and the second refrigerant flow switching device 18 b(2)) are disposed downstream of the heat exchanger related to heat medium 15 b, downstream regarding the heat source side refrigerant flow during the cooling only operation mode.

The two pumps 21 (a pump 21 a and a pump 21 b) circulate the heat medium flowing through the piping 5. The pump 21 a is disposed in the piping 5 between the heat exchanger related to heat medium 15 a and the second heat medium flow switching devices 23. The pump 21 b is disposed in the piping 5 between the heat exchanger related to heat medium 15 b and the second heat medium flow switching devices 23. Each of the two pumps 21 may include, for example, a capacity-controllable pump. Note that the pump 21 a may be provided in the piping 5 between the heat exchanger related to heat medium 15 a and the first heat medium flow switching devices 22. Furthermore, the pump 21 b may be provided in the piping 5 between the heat exchanger related to heat medium 15 b and the first heat medium flow switching devices 22.

The four first heat medium flow switching devices 22 (first heat medium flow switching devices 22 a to 22 d) each include, for example, a three-way valve and switch passages of the heat medium. The first heat medium flow switching devices 22 are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units 2. Each first heat medium flow switching device 22 is disposed on an outlet side of a heat medium passage of the corresponding use side heat exchanger 26 such that one of the three ways is connected to the heat exchanger related to heat medium 15 a, another one of the three ways is connected to the heat exchanger related to heat medium 15 b, and the other one of the three ways is connected to the heat medium flow control device 25. Furthermore, illustrated from the bottom of the drawing are the first heat medium flow switching device 22 a, the first heat medium flow switching device 22 b, the first heat medium flow switching device 22 c, and the first heat medium flow switching device 22 d, so as to correspond to the respective indoor units 2.

The four second heat medium flow switching devices 23 (second heat medium flow switching devices 23 a to 23 d) each include, for example, a three-way valve and are configured to switch passages of the heat medium. The second heat medium flow switching devices 23 are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units 2. Each second heat medium flow switching device 23 is disposed on an inlet side of the heat medium passage of the corresponding use side heat exchanger 26 such that one of the three ways is connected to the heat exchanger related to heat medium 15 a, another one of the three ways is connected to the heat exchanger related to heat medium 15 b, and the other one of the three ways is connected to the use side heat exchanger 26. Furthermore, illustrated from the bottom of the drawing are the second heat medium flow switching device 23 a, the second heat medium flow switching device 23 b, the second heat medium flow switching device 23 c, and the second heat medium flow switching device 23 d so as to correspond to the respective indoor units 2.

The four heat medium flow control devices 25 (heat medium flow control devices 25 a to 25 d) each include, for example, a two-way valve capable of controlling the area of opening and controls the flow rate of the heat medium flowing in piping 5. The heat medium flow control devices 25 are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units 2. Each heat medium flow control device 25 is disposed on the outlet side of the heat medium passage of the corresponding use side heat exchanger 26 such that one way is connected to the use side heat exchanger 26 and the other way is connected to the first heat medium flow switching device 22. Furthermore, illustrated from the bottom of the drawing are the heat medium flow control device 25 a, the heat medium flow control device 25 b, the heat medium flow control device 25 c, and the heat medium flow control device 25 d so as to correspond to the respective indoor units 2. In addition, each of the heat medium flow control devices 25 may be disposed on the inlet side of the heat medium passage of the corresponding use side heat exchanger 26.

The heat medium relay unit 3 includes various detecting means (two first temperature sensors 31, four second temperature sensors 34, four third temperature sensors 35, a pressure sensor 36, and a concentration detection device 39). Information (temperature information, pressure information, and concentration information of the heat source side refrigerant, for example) detected by these detecting means are transmitted to a controller (not illustrated) that performs integrated control of the operation of the air-conditioning apparatus 101 such that the information is used to control, for example, the driving frequency of the compressor 10, the rotation speed of the air-moving device (not illustrated) provided in the vicinity of the heat source side heat exchanger 12 and each use side heat exchanger 26, switching of the first refrigerant flow switching device 11, the driving frequency of the pumps 21, switching of the second refrigerant flow switching devices 18, opening and closing of the first shut off device 37, opening and closing of the second shut off device 38, and switching of passages of the heat medium.

Each of the two first temperature sensors 31 (a first temperature sensor 31 a and a first temperature sensor 31 b) detects the temperature of the heat medium flowing out of the corresponding heat exchanger related to heat medium 15, namely, the heat medium at the outlet of the corresponding heat exchanger related to heat medium 15 and may include, for example, a thermistor. The first temperature sensor 31 a is disposed in the piping 5 on the inlet side of the pump 21 a. The first temperature sensor 31 b is disposed in the piping 5 on the inlet side of the pump 21 b.

Each of the four second temperature sensors 34 (second temperature sensor 34 a to 34 d) is disposed between the first heat medium flow switching device 22 and the heat medium flow control device 25 and detects the temperature of the heat medium flowing out of the use side heat exchanger 26. A thermistor or the like may be used as the second temperature sensor 34. The second temperature sensors 34 are arranged so that the number (four in this case) corresponds to the installed number of indoor units 2. Furthermore, illustrated from the bottom of the drawing are the second temperature sensor 34 a, the second temperature sensor 34 b, the second temperature sensor 34 c, and the second temperature sensor 34 d so as to correspond to the respective indoor units 2.

Each of the four third temperature sensors 35 (third temperature sensors 35 a to 35 d) is disposed on the inlet side or the outlet side of a heat source side refrigerant of the heat exchanger related to heat medium 15 and detects the temperature of the heat source side refrigerant flowing into the heat exchanger related to heat medium 15 or the temperature of the heat source side refrigerant flowing out of the heat exchanger related to heat medium 15 and may include, for example, a thermistor. The third temperature sensor 35 a is disposed between the heat exchanger related to heat medium 15 a and the second refrigerant flow switching device 18 a. The third temperature sensor 35 b is disposed between the heat exchanger related to heat medium 15 a and the expansion device 16 a. The third temperature sensor 35 c is disposed between the heat exchanger related to heat medium 15 b and the second refrigerant flow switching device 18 b. The third temperature sensor 35 d is disposed between the heat exchanger related to heat medium 15 b and the expansion device 16 b.

The pressure sensor 36 is disposed between the heat exchanger related to heat medium 15 b and the expansion device 16 b, similar to the installation position of the third temperature sensor 35 d, and is configured to detect the pressure of the heat source side refrigerant flowing between the heat exchanger related to heat medium 15 b and the expansion device 16 b.

Concentration detection devices 39 detect the concentration of the refrigerant in the heat medium relay unit 3.

Further, the controller (not illustrated) includes, for example, a microcomputer and controls, for example, the driving frequency of the compressor 10, the rotation speed (including ON/OFF) of the air-moving devices, switching of the first refrigerant flow switching device 11, driving of the pumps 21, the opening degree of each expansion device 16, opening and closing of the first shut off device 37, opening and closing of the second shut off device 38, closing and opening of the on-off device 17, switching of the second refrigerant flow switching devices 18, switching of the first heat medium flow switching devices 22, switching of the second heat medium flow switching devices 23, and the opening degree of each heat medium flow control device 25, on the basis of the information detected by the various detecting means and an instruction from a remote control to carry out the operation modes which will be described later. Note that the controller may be provided to each unit, or may be provided to the outdoor unit 1 or the heat medium relay unit 3.

The pipings 5 in which the heat medium flows include the pipings connected to the heat exchanger related to heat medium 15 a and the pipings connected to the heat exchanger related to heat medium 15 b. Each piping 5 is branched (into four in this case) in accordance with the number of indoor units 2 connected to the heat medium relay unit 3. The pipings 5 are connected by the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23. Controlling the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 determines whether the heat medium flowing from the heat exchanger related to heat medium 15 a is allowed to flow into the use side heat exchanger 26 or whether the heat medium flowing from the heat exchanger related to heat medium 15 b is allowed to flow into the use side heat exchanger 26.

In the air-conditioning apparatus 101, the compressor 10, the first refrigerant flow switching device 11, the heat source side heat exchanger 12, the first shut off device 37, the on-off device 17, the second refrigerant flow switching devices 18, a refrigerant passage of the heat exchanger related to heat medium 15 a, the expansion devices 16, the second shut off device 38, and the accumulator 19 are connected through the refrigerant piping 4, thus forming the refrigerant circuit A. In addition, a heat medium passage of the heat exchanger related to heat medium 15 a, the pumps 21, the first heat medium flow switching devices 22, the heat medium flow control devices 25, the use side heat exchangers 26, and the second heat medium flow switching devices 23 are connected through the pipings 5, thus forming the heat medium circuit B. In other words, the plurality of use side heat exchangers 26 are connected in parallel to each of the heat exchangers related to heat medium 15, thus turning the heat medium circuit B into a multi-system.

Accordingly, in the air-conditioning apparatus 101, the outdoor unit 1 and the heat medium relay unit 3 are connected through the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b arranged in the heat medium relay unit 3. The heat medium relay unit 3 and each indoor unit 2 are connected through the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b. In other words, in the air-conditioning apparatus 101, the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b each exchange heat between the heat source side refrigerant circulating in the refrigerant circuit A and the heat medium circulating in the heat medium circuit B.

Various operation modes executed by the air-conditioning apparatus 101 will be described below. The air-conditioning apparatus 101 allows each indoor unit 2, on the basis of an instruction from the indoor unit 2, to perform a cooling operation or heating operation. Specifically, the air-conditioning apparatus 101 may allow all of the indoor units 2 to perform the same operation and also allow each of the indoor units 2 to perform different operations.

The operation modes carried out by the air-conditioning apparatus 101 includes a cooling only operation mode in which all of the operating indoor units 2 perform the cooling operation, a heating only operation mode in which all of the operating indoor units 2 perform the heating operation, a cooling main operation mode that is a cooling and heating mixed operation mode in which cooling load is larger, and a heating main operation mode that is a cooling and heating mixed operation mode in which heating load is larger. The operation modes will be described below with respect to the flow of the heat source side refrigerant and that of the heat medium.

Cooling Only Operation Mode

FIG. 8 is a refrigerant circuit diagram illustrating the flows of refrigerants in the cooling only operation mode of the air-conditioning apparatus 101. The cooling only operation mode will be described with respect to a case in which cooling loads are generated only in the use side heat exchanger 26 a and the use side heat exchanger 26 b in FIG. 8. Furthermore, in FIG. 8, pipings indicated by thick lines indicate pipings through which the refrigerants (the heat source side refrigerant and the heat medium) flow. In addition, the direction of flow of the heat source side refrigerant is indicated by solid-line arrows and the direction of flow of the heat medium is indicated by broken-line arrows in FIG. 8.

In the cooling only operation mode illustrated in FIG. 8, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source side refrigerant discharged from the compressor 10 flows into the heat source side heat exchanger 12. In the heat medium relay unit 3, the pump 21 a and the pump 21 b are driven, the heat medium flow control device 25 a and the heat medium flow control device 25 b are opened, and the heat medium flow control device 25 c and the heat medium flow control device 25 d are fully closed such that the heat medium circulates between each of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b and each of the use side heat exchanger 26 a and the use side heat exchanger 26 b.

First, the flow of the heat source side refrigerant in the refrigerant circuit A will be described.

A low-temperature low-pressure refrigerant is compressed by the compressor 10 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant discharged from the compressor 10 flows through the first refrigerant flow switching device 11 into the heat source side heat exchanger 12. Then, the refrigerant turns into a high-pressure refrigerant that has lowered its temperature in a supercritical state while transferring heat to outdoor air in the heat source side heat exchanger 12. The high-pressure refrigerant flowing out of the heat source side heat exchanger 12, flows out of the outdoor unit 1, passes through the refrigerant piping 4, and flows into the heat medium relay unit 3. The high-pressure refrigerant that has flowed into the heat medium relay unit 3 is branched after passing through the first shut off device 37 and the on-off device 17 and is expanded into a low-temperature low-pressure two-phase refrigerant by the expansion device 16 a and the expansion device 16 b. Note that the on-off device 17 is opened.

This two-phase refrigerant flows into each of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b, functioning as evaporators, removes heat from the heat medium circulating in the heat medium circuit B, cools the heat medium, and turns into a low-temperature low-pressure gas refrigerant. The gas refrigerant, which has flowed out of each of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b, passes through the second refrigerant flow switching device 18 a(1) and the second refrigerant flow switching device 18 b(1), respectively, and passes through the second shut off device 38, flows out of the heat medium relay unit 3, passes through the refrigerant piping 4, and flows into the outdoor unit 1 again. The refrigerant that has flowed into the outdoor unit 1 passes through the first refrigerant flow switching device 11 and the accumulator 19 and is sucked into the compressor 10 again.

Here, the second refrigerant flow switching devices 18 a(1) and 18 b(1) are opened and the second refrigerant flow switching devices 18 a(2) and 18 b(2) are closed. Since the second refrigerant flow switching devices 18 a(2) and 18 b(2) are both closed, there is no refrigerant flow in a bypass piping 4 d (the refrigerant piping 4 that allows bypass of the heat exchangers related to heat medium 15 by connecting the portion between the first shut off device 37 and the on-off device 17 to the second refrigerant flow switching devices 18 a(2) and 18 b(2)). Note that one end of the bypass piping 4 d is in a high-pressure state and the bypass piping is filled with a high-pressure heat source side refrigerant.

Further, the opening degree of the expansion device 16 a is controlled such that superheat (the degree of superheat) is constant, in which the superheat is obtained as the difference between a temperature detected by the third temperature sensor 35 a and that detected by the third temperature sensor 35 b. Similarly, the opening degree of the expansion device 16 b is controlled such that superheat is constant, in which the superheat is obtained as the difference between a temperature detected by a third temperature sensor 35 c and that detected by a third temperature sensor 35 d.

Next, the flow of the heat medium in the heat medium circuit B will be described.

In the cooling only operation mode, both the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b transfer cooling energy of the heat source side refrigerant to the heat medium, and the pump 21 a and the pump 21 b allow the cooled heat medium to flow through the pipings 5. The heat medium, which has flowed out of each of the pump 21 a and the pump 21 b while being pressurized, flows through the second heat medium flow switching device 23 a and the second heat medium flow switching device 23 b into the use side heat exchanger 26 a and the use side heat exchanger 26 b. The heat medium removes heat from the indoor air in each of the use side heat exchanger 26 a and the use side heat exchanger 26 b, thus cools the indoor space 7.

The heat medium then flows out of the use side heat exchanger 26 a and the use side heat exchanger 26 b and flows into the heat medium flow control device 25 a and the heat medium flow control device 25 b. At this time, the function of each of the heat medium flow control device 25 a and the heat medium flow control device 25 b allows the heat medium to flow into the corresponding one of the use side heat exchanger 26 a and the use side heat exchanger 26 b while controlling the heat medium to a flow rate sufficient to cover an air conditioning load required in the indoor space. The heat medium, which has flowed out of the heat medium flow control device 25 a and the heat medium flow control device 25 b, passes through the first heat medium flow switching device 22 a and the first heat medium flow switching device 22 b, respectively, flows into the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b, and is again sucked into the pump 21 a and the pump 21 b.

Note that in the pipings 5 of each use side heat exchanger 26, the heat medium is directed to flow from the second heat medium flow switching device 23 through the heat medium flow control device 25 to the first heat medium flow switching device 22. The air conditioning load required in the indoor space 7 can be satisfied by controlling the difference between a temperature detected by the first temperature sensor 31 a or a temperature detected by the first temperature sensor 31 b and a temperature detected by the second temperature sensor 34 so that difference is maintained at a target value. As regards a temperature at the outlet of each heat exchanger related to heat medium 15, either of the temperature detected by the first temperature sensor 31 a or that detected by the first temperature sensor 31 b may be used. Alternatively, the mean temperature of the two may be used. At this time, the opening degree of each of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 is set to a medium degree such that passages to both of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b are established.

Upon carrying out the cooling only operation mode, since it is unnecessary to supply the heat medium to each use side heat exchanger 26 having no heat load (including thermo-off), the passage is closed by the corresponding heat medium flow control device 25 such that the heat medium does not flow into the corresponding use side heat exchanger 26. In FIG. 8, the heat medium is supplied to the use side heat exchanger 26 a and the use side heat exchanger 26 b because these use side heat exchangers have heat loads. The use side heat exchanger 26 c and the use side heat exchanger 26 d have no heat load and the corresponding heat medium flow control devices 25 c and 25 d are fully closed. When a heat load is generated in the use side heat exchanger 26 c or the use side heat exchanger 26 d, the heat medium flow control device 25 c or the heat medium flow control device 25 d may be opened such that the heat medium is circulated.

Heating Only Operation Mode

FIG. 9 is a refrigerant circuit diagram illustrating the flows of the refrigerants in the heating only operation mode of the air-conditioning apparatus 101. The heating only operation mode will be described with respect to a case in which heating loads are generated only in the use side heat exchanger 26 a and the use side heat exchanger 26 b in FIG. 9. Furthermore, in FIG. 9, pipings indicated by thick lines indicate pipings through which the refrigerants (the heat source side refrigerant and the heat medium) flow. In addition, the direction of flow of the heat source side refrigerant is indicated by solid-line arrows and the direction of flow of the heat medium is indicated by broken-line arrows in FIG. 9.

In the heating only operation mode illustrated in FIG. 9, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source side refrigerant discharged from the compressor 10 flows into the heat medium relay unit 3 without passing through the heat source side heat exchanger 12. In the heat medium relay unit 3, the pump 21 a and the pump 21 b are driven, the heat medium flow control device 25 a and the heat medium flow control device 25 b are opened, and the heat medium flow control device 25 c and the heat medium flow control device 25 d are fully closed such that the heat medium circulates between each of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b and each of the use side heat exchanger 26 a and the use side heat exchanger 26 b.

First, the flow of the heat source side refrigerant in the refrigerant circuit A will be described.

A low-temperature low-pressure refrigerant is compressed by the compressor 10 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant discharged from the compressor 10 passes through the first refrigerant flow switching device 11 and flows out of the outdoor unit 1. The high-temperature high-pressure gas refrigerant that has flowed out of the outdoor unit 1 passes through the refrigerant piping 4 and flows into the heat medium relay unit 3. The high-temperature high-pressure gas refrigerant that has flowed into the heat medium relay unit 3 is branched after passing through the second shut off device 38, passes through the second refrigerant flow switching device 18 a(1) and the second refrigerant flow switching device 18 b(1), and flows into the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b, respectively.

The high-temperature high-pressure gas refrigerant that has flowed into the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b turns into a high-pressure refrigerant that has lowered its temperature in a supercritical state while transferring heat to the heat medium circulating in the heat medium circuit B. The liquid refrigerant flowing out of the heat exchanger related to heat medium 15 a and that flowing out of the heat exchanger related to heat medium 15 b are expanded into a low-temperature low-pressure, two-phase refrigerant in the expansion device 16 a and the expansion device 16 b. This two-phase refrigerant passes through the on-off device 17 and the first shut off device 37, flows out of the heat medium relay unit 3, passes through the refrigerant piping 4, and flows into the outdoor unit 1 again. Note that the on-off device 17 is opened.

The refrigerant flowing into the outdoor unit 1 flows into the heat source side heat exchanger 12, functioning as an evaporator. Then, the refrigerant that has flowed into the heat source side heat exchanger 12 removes heat from the outdoor air in the heat source side heat exchanger 12 and turns into a low-temperature low-pressure gas refrigerant. The low-temperature low-pressure gas refrigerant flowing out of the heat source side heat exchanger 12 passes through the first refrigerant flow switching device 11 and the accumulator 19 and is sucked into the compressor 10 again.

Here, the second refrigerant flow switching devices 18 a(1) and 18 b(1) are opened and the second refrigerant flow switching devices 18 a(2) and 18 b(2) are closed. Since the second refrigerant flow switching devices 18 a(2) and 18 b(2) are closed, there will be no refrigerant flow in the bypass piping 4 d. However, one end of the bypass piping 4 d is a low-pressure two-phase pipe, and the bypass piping is filled with a low-pressure refrigerant.

Further, the opening degree of the expansion device 16 a is controlled such that subcooling (degree of subcooling) obtained as the difference between a saturation temperature converted from a pressure detected by the pressure sensor 36 and a temperature detected by the third temperature sensor 35 b is constant. Similarly, the opening degree of the expansion device 16 b is controlled such that subcooling is constant, in which the subcooling is obtained as the difference between the value indicating the saturation temperature converted from the pressure detected by the pressure sensor 36 and a temperature detected by the third temperature sensor 35 d. Note that when a temperature at the middle position of the heat exchangers related to heat medium 15 can be measured, the temperature at the middle position may be used instead of the pressure sensor 36. Accordingly, the system can be constructed inexpensively.

Next, the flow of the heat medium in the heat medium circuit B will be described.

In the heating only operation mode, both of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b transfer heating energy of the heat source side refrigerant to the heat medium, and the pump 21 a and the pump 21 b allow the heated heat medium to flow through the pipings 5. The heat medium, which has flowed out of each of the pump 21 a and the pump 21 b while being pressurized, flows through the second heat medium flow switching device 23 a and the second heat medium flow switching device 23 b into the use side heat exchanger 26 a and the use side heat exchanger 26 b. Then the heat medium transfers heat to the indoor air in the use side heat exchanger 26 a and the use side heat exchanger 26 b, thus heats the indoor space 7.

The heat medium then flows out of the use side heat exchanger 26 a and the use side heat exchanger 26 b and flows into the heat medium flow control device 25 a and the heat medium flow control device 25 b, respectively. At this time, the function of each of the heat medium flow control device 25 a and the heat medium flow control device 25 b allows the heat medium to flow into the corresponding one of the use side heat exchanger 26 a and the use side heat exchanger 26 b while controlling the heat medium to a flow rate sufficient to cover an air conditioning load required in the indoor space. The heat medium, which has flowed out of the heat medium flow control device 25 a and the heat medium flow control device 25 b, passes through the first heat medium flow switching device 22 a and the first heat medium flow switching device 22 b, respectively, flows into the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b, and is again sucked into the pump 21 a and the pump 21 b.

Note that in the pipings 5 of each use side heat exchanger 26, the heat medium is directed to flow from the second heat medium flow switching device 23 through the heat medium flow control device 25 to the first heat medium flow switching device 22. The air conditioning load required in the indoor space 7 can be satisfied by controlling the difference between a temperature detected by the first temperature sensor 31 a or a temperature detected by the first temperature sensor 31 b and a temperature detected by the second temperature sensor 34 so that difference is maintained at a target value. As regards a temperature at the outlet of each heat exchanger related to heat medium 15, either of the temperature detected by the first temperature sensor 31 a or that detected by the first temperature sensor 31 b may be used. Alternatively, the mean temperature of the two may be used.

At this time, the opening degree of each of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 are set to a medium degree such that passages to both of the heat exchanger related to heat medium 15 a and the heat exchanger related to heat medium 15 b are established. Although the use side heat exchanger 26 a should essentially be controlled on the basis of the difference between a temperature at its inlet and that at its outlet, since the temperature of the heat medium on the inlet side of the use side heat exchanger 26 is substantially the same as that detected by the first temperature sensor 31 b, the use of the first temperature sensor 31 b can reduce the number of temperature sensors, so that the system can be constructed inexpensively.

Upon carrying out the heating only operation mode, since it is unnecessary to supply the heat medium to each use side heat exchanger 26 having no heat load (including thermo-off), the passage is closed by the corresponding heat medium flow control device 25 such that the heat medium does not flow into the corresponding use side heat exchanger 26.

In FIG. 9, the heat medium is supplied to the use side heat exchanger 26 a and the use side heat exchanger 26 b because these use side heat exchangers have heat loads. The use side heat exchanger 26 c and the use side heat exchanger 26 d have no heat load and the corresponding heat medium flow control devices 25 c and 25 d are fully closed. When a heat load is generated in the use side heat exchanger 26 c or the use side heat exchanger 26 d, the heat medium flow control device 25 c or the heat medium flow control device 25 d may be opened such that the heat medium is circulated.

Cooling Main Operation Mode

FIG. 10 is a refrigerant circuit diagram illustrating the flows of the refrigerants in the cooling main operation mode of the air-conditioning apparatus 101. The cooling main operation mode will be described with respect to a case in which a cooling load is generated in the use side heat exchanger 26 a and a heating load is generated in the use side heat exchanger 26 b in FIG. 10. Furthermore, in FIG. 10, pipings indicated by thick lines correspond to pipings through which the refrigerants (the heat source side refrigerant and the heat medium) circulate. In addition, the direction of flow of the heat source side refrigerant is indicated by solid-line arrows and the direction of flow of the heat medium is indicated by broken-line arrows in FIG. 10.

In the cooling main operation mode illustrated in FIG. 10, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source side refrigerant discharged from the compressor 10 flows into the heat source side heat exchanger 12. In the heat medium relay unit 3, the pump 21 a and the pump 21 b are driven, the heat medium flow control device 25 a and the heat medium flow control device 25 b are opened, and the heat medium flow control device 25 c and the heat medium flow control device 25 d are fully closed such that the heat medium circulates between the heat exchanger related to heat medium 15 a and the use side heat exchanger 26 a, and between the heat exchanger related to heat medium 15 b and the use side heat exchanger 26 b.

First, the flow of the heat source side refrigerant in the refrigerant circuit A will be described.

A low-temperature low-pressure refrigerant is compressed by the compressor 10 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant discharged from the compressor 10 flows through the first refrigerant flow switching device 11 into the heat source side heat exchanger 12. Then, the refrigerant is turned into a refrigerant that has lowered its temperature in a supercritical state while transferring heat to outdoor air in the heat source side heat exchanger 12. The refrigerant flowing out of the heat source side heat exchanger 12, flows out of the outdoor unit 1, passes through the refrigerant piping 4, and flows into the heat medium relay unit 3. The two-phase refrigerant that has flowed into the heat medium relay unit 3 passes through the bypass pipe 4 d and the second refrigerant flow switching device 18 b(2), and flows into the heat exchanger related to heat medium 15 b, functioning as a condenser (gas cooler).

The refrigerant that has flowed into the heat exchanger related to heat medium 15 b turns into a refrigerant that has further lowered its temperature while transferring heat to the heat medium circulating in the heat medium circuit B. The refrigerant flowing out of the heat exchanger related to heat medium 15 b is expanded into a low-pressure two-phase refrigerant by the expansion device 16 b. This low-pressure two-phase refrigerant flows through the expansion device 16 a into the heat exchanger related to heat medium 15 a, functioning as an evaporator. The low-pressure two-phase refrigerant flowing into the heat exchanger related to heat medium 15 a removes heat from the heat medium circulating in the heat medium circuit B, cools the heat medium, and turns into a low-pressure gas refrigerant. The gas refrigerant flows out of the heat exchanger related to heat medium 15 a, passes through the second refrigerant flow switching device 18 a(1) and the second shut off device 38, flows out of the heat medium relay unit 3, and flows into the outdoor unit 1 again through the refrigerant piping 4. The refrigerant that has flowed into the outdoor unit 1 passes through the first refrigerant flow switching device 11 and the accumulator 19 and is sucked into the compressor 10 again.

Here, the second refrigerant flow switching device 18 a(1) is opened, the second refrigerant flow switching device 18 a(2) is closed, the second refrigerant flow switching device 18 b(1) is closed, and the second refrigerant flow switching device 18 b(2) is opened. Since the second refrigerant flow switching device 18 a(2) is closed and the second refrigerant flow switching device 18 b(2) is opened, a high-pressure refrigerant flows in the bypass piping 4 d and the bypass piping 4 d is filled with the high-pressure heat source side refrigerant.

Further, the opening degree of the expansion device 16 b is controlled such that superheat is constant, in which the superheat is obtained as the difference between a temperature detected by the third temperature sensor 35 a and that detected by the third temperature sensor 35 b. Furthermore, the expansion device 16 a is fully opened and the on-off device 17 is closed. Note that the opening degree of the expansion device 16 b may be controlled such that subcooling is constant, in which the subcooling is obtained as the difference between a value indicating a saturation temperature converted from a pressure detected by the pressure sensor 36 and a temperature detected by the third temperature sensor 35 d. Alternatively, the expansion device 16 b may be fully opened and the expansion device 16 a may control the superheat or the subcooling.

Next, the flow of the heat medium in the heat medium circuit B will be described.

In the cooling main operation mode, the heat exchanger related to heat medium 15 b transfers heating energy of the heat source side refrigerant to the heat medium, and the pump 21 b allows the heated heat medium to flow through the pipings 5. Furthermore, in the cooling main operation mode, the heat exchanger related to heat medium 15 a transfers cooling energy of the heat source side refrigerant to the heat medium, and the pump 21 a allows the cooled heat medium to flow through the pipings 5. The heat medium that has flowed out of each of the pump 21 a and the pump 21 b while being pressurized, flows through the second heat medium flow switching device 23 a and the second heat medium flow switching device 23 b into the use side heat exchanger 26 a and the use side heat exchanger 26 b.

In the use side heat exchanger 26 b, the heat medium transfers heat to the indoor air, thus heats the indoor space 7. In addition, in the use side heat exchanger 26 a, the heat medium removes heat from the indoor air, thus cools the indoor space 7. At this time, the function of each of the heat medium flow control device 25 a and the heat medium flow control device 25 b allows the heat medium to flow into the corresponding one of the use side heat exchanger 26 a and the use side heat exchanger 26 b while controlling the heat medium to a flow rate sufficient to cover an air conditioning load required in the indoor space. The heat medium, which has passed through the use side heat exchanger 26 b with a slight decrease of temperature, passes through the heat medium flow control device 25 b and the first heat medium flow switching device 22 b, flows into the heat exchanger related to heat medium 15 b, and is sucked into the pump 21 b again. The heat medium, which has passed through the use side heat exchanger 26 a with a slight increase of temperature, passes through the heat medium flow control device 25 a and the first heat medium flow switching device 22 a, flows into the heat exchanger related to heat medium 15 a, and is then sucked into the pump 21 a again.

During this time, the function of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 allow the heated heat medium and the cooled heat medium to be introduced into the respective use side heat exchangers 26 having a heating load and a cooling load, without being mixed. Note that in the pipings 5 of each of the use side heat exchanger 26 for heating and that for cooling, the heat medium is directed to flow from the second heat medium flow switching device 23 through the heat medium flow control device 25 to the first heat medium flow switching device 22. Furthermore, the difference between the temperature detected by the first temperature sensor 31 b and that detected by the second temperature sensor 34 is controlled such that the difference is kept at a target value, so that the heating air conditioning load required in the indoor space 7 can be covered. The difference between the temperature detected by the second temperature sensor 34 and that detected by the first temperature sensor 31 a is controlled such that the difference is kept at a target value, so that the cooling air conditioning load required in the indoor space 7 can be covered.

Upon carrying out the cooling main operation mode, since it is unnecessary to supply the heat medium to each use side heat exchanger 26 having no heat load (including thermo-off), the passage is closed by the corresponding heat medium flow control device 25 such that the heat medium does not flow into the corresponding use side heat exchanger 26. In FIG. 10, the heat medium is supplied to the use side heat exchanger 26 a and the use side heat exchanger 26 b because these use side heat exchangers have heat loads. The use side heat exchanger 26 c and the use side heat exchanger 26 d have no heat load and the corresponding heat medium flow control devices 25 c and 25 d are fully closed. When a heat load is generated in the use side heat exchanger 26 c or the use side heat exchanger 26 d, the heat medium flow control device 25 c or the heat medium flow control device 25 d may be opened such that the heat medium is circulated.

Heating Main Operation Mode

FIG. 11 is a refrigerant circuit diagram illustrating the flows of the refrigerants in the heating main operation mode of the air-conditioning apparatus 101. The heating main operation mode will be described with respect to a case in which a heating load is generated in the use side heat exchanger 26 a and a cooling load is generated in the use side heat exchanger 26 b in FIG. 11. Furthermore, in FIG. 11, pipings indicated by thick lines correspond to pipings through which the refrigerants (the heat source side refrigerant and the heat medium) circulate. In addition, the direction of flow of the heat source side refrigerant is indicated by solid-line arrows and the direction of flow of the heat medium is indicated by broken-line arrows in FIG. 11.

In the heating main operation mode illustrated in FIG. 11, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source side refrigerant discharged from the compressor 10 flows into the heat medium relay unit 3 without passing through the heat source side heat exchanger 12. In the heat medium relay unit 3, the pump 21 a and the pump 21 b are driven, the heat medium flow control device 25 a and the heat medium flow control device 25 b are opened, and the heat medium flow control device 25 c and the heat medium flow control device 25 d are fully closed such that the heat medium circulates between the heat exchanger related to heat medium 15 a and the use side heat exchanger 26 b, and between the heat exchanger related to heat medium 15 b and the use side heat exchanger 26 a.

First, the flow of the heat source side refrigerant in the refrigerant circuit A will be described.

A low-temperature low-pressure refrigerant is compressed by the compressor 10 and is discharged as a high-temperature high-pressure gas refrigerant therefrom. The high-temperature high-pressure gas refrigerant discharged from the compressor 10 passes through the first refrigerant flow switching device 11 and flows out of the outdoor unit 1. The high-temperature high-pressure gas refrigerant that has flowed out of the outdoor unit 1 passes through the refrigerant piping 4 and flows into the heat medium relay unit 3. The high-temperature high-pressure gas refrigerant that has flowed into the heat medium relay unit 3 passes through the second shut off device 38 and the second refrigerant flow switching device 18 b(1) and flows into the heat exchanger related to heat medium 15 b, functioning as a condenser (gas cooler).

The gas refrigerant that has flowed into the heat exchanger related to heat medium 15 b is turned into a refrigerant that has lowered its temperature in a supercritical state while transferring heat to the heat medium circulating in the heat medium circuit B. The refrigerant flowing out of the heat exchanger related to heat medium 15 b is expanded into a low-pressure two-phase refrigerant by the expansion device 16 b. This low-pressure two-phase refrigerant flows through the expansion device 16 a and into the heat exchanger related to heat medium 15 a, functioning as an evaporator. The low-pressure two-phase refrigerant that has flowed into the heat exchanger related to heat medium 15 a removes heat from the heat medium circulating in the heat medium circuit B, is evaporated, and cools the heat medium. This low-pressure two-phase refrigerant flows out of the heat exchanger related to heat medium 15 a, passes through the first shut off device 37 through the second refrigerant flow switching device 18 a(2) and the bypass piping 4 d, flows out of the heat medium relay unit 3, passes through the refrigerant piping 4, and flows into the outdoor unit 1 again.

The refrigerant that has flowed into the outdoor unit 1 flows into the heat source side heat exchanger 12, functioning as an evaporator. Then, the refrigerant that has flowed into the heat source side heat exchanger 12 removes heat from the outdoor air in the heat source side heat exchanger 12 and turns into a low-temperature low-pressure gas refrigerant. The low-temperature low-pressure gas refrigerant flowing out of the heat source side heat exchanger 12 passes through the first refrigerant flow switching device 11 and the accumulator 19 and is sucked into the compressor 10 again.

Here, the second refrigerant flow switching device 18 a(1) is closed, the second refrigerant flow switching device 18 a(2) is opened, the second refrigerant flow switching device 18 b(1) is opened, and the second refrigerant flow switching device 18 b(2) is closed. Since the second refrigerant flow switching device 18 a(2) is opened and the second refrigerant flow switching device 18 b(2) is closed, a low-pressure two-phase refrigerant flows in the bypass piping 4 d, and the bypass piping 4 d is filled with low-pressure heat source side refrigerant.

Further, the opening degree of the expansion device 16 b is controlled such that subcooling is constant, in which the subcooling is obtained as the difference between a value indicating a saturation temperature converted from a pressure detected by the pressure sensor 36 and a temperature detected by the third temperature sensor 35 b. Furthermore, the expansion device 16 a is fully opened and the on-off device 17 is closed. Alternatively, the expansion device 16 b may be fully opened and the expansion device 16 a may control the subcooling.

Next, the flow of the heat medium in the heat medium circuit B will be described.

In the heating main operation mode, the heat exchanger related to heat medium 15 b transfers heating energy of the heat source side refrigerant to the heat medium, and the pump 21 b allows the heated heat medium to flow through the pipings 5. Furthermore, in the heating main operation mode, the heat exchanger related to heat medium 15 a transfers cooling energy of the heat source side refrigerant to the heat medium, and the pump 21 a allows the cooled heat medium to flow through the pipings 5. The heat medium, which has flowed out of each of the pump 21 a and the pump 21 b while being pressurized, flows through the second heat medium flow switching device 23 a and the second heat medium flow switching device 23 b into the use side heat exchanger 26 a and the use side heat exchanger 26 b.

In the use side heat exchanger 26 b, the heat medium removes heat from the indoor air, thus cools the indoor space 7. In addition, in the use side heat exchanger 26 a, the heat medium transfers heat to the indoor air, thus heats the indoor space 7. At this time, the function of each of the heat medium flow control device 25 a and the heat medium flow control device 25 b allows the heat medium to flow into the corresponding one of the use side heat exchanger 26 a and the use side heat exchanger 26 b while controlling the heat medium to a flow rate sufficient to cover an air conditioning load required in the indoor space. The heat medium, which has passed through the use side heat exchanger 26 b with a slight increase of temperature, passes through the heat medium flow control device 25 b and the first heat medium flow switching device 22 b, flows into the heat exchanger related to heat medium 15 a, and is sucked into the pump 21 a again. The heat medium, which has passed through the use side heat exchanger 26 a with a slight decrease of temperature, passes through the heat medium flow control device 25 a and the first heat medium flow switching device 22 a, flows into the heat exchanger related to heat medium 15 b, and is then sucked into the pump 21 b again.

During this time, the function of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 allow the heated heat medium and the cooled heat medium to be introduced into the respective use side heat exchangers 26 having a heating load and a cooling load, without being mixed. Note that in the pipings 5 of each of the use side heat exchanger 26 for heating and that for cooling, the heat medium is directed to flow from the second heat medium flow switching device 23 through the heat medium flow control device 25 to the first heat medium flow switching device 22. Furthermore, the difference between the temperature detected by the first temperature sensor 31 b and that detected by the second temperature sensor 34 is controlled such that the difference is kept at a target value, so that the heating air conditioning load required in the indoor space 7 can be covered. The difference between the temperature detected by the second temperature sensor 34 and that detected by the first temperature sensor 31 a is controlled such that the difference is kept at a target value, so that the cooling air conditioning load required in the indoor space 7 can be covered.

Upon carrying out the heating main operation mode, since it is unnecessary to supply the heat medium to each use side heat exchanger 26 having no heat load (including thermo-off), the passage is closed by the corresponding heat medium flow control device 25 such that the heat medium does not flow into the corresponding use side heat exchanger 26. In FIG. 7, the heat medium is supplied to the use side heat exchanger 26 a and the use side heat exchanger 26 b because these use side heat exchangers have heat loads. The use side heat exchanger 26 c and the use side heat exchanger 26 d have no heat load and the corresponding heat medium flow control devices 25 c and 25 d are fully closed. When a heat load is generated in the use side heat exchanger 26 c or the use side heat exchanger 26 d, the heat medium flow control device 25 c or the heat medium flow control device 25 d may be opened such that the heat medium is circulated.

The configuration and operation of the first shut off device 37, the second shut off device 38, and the concentration detection device 39 are the same as that of the first shut off devices 303, the second shut off devices 304, and the concentration detection devices 305, respectively, of the air-conditioning apparatus 100 according to Embodiment 1. Further, the basic specification of the air-conditioning apparatus 101 according to Embodiment 2, such as the power driving method, the minimum operating pressure differential, the amount of leakage, and the like, are the same as that of the air-conditioning apparatus according to Embodiment 1. Additionally, assuming cases of a blackout or failure of electric power supply from a commercial power supply to the concentration detection device 39, by using one that can be operated by a battery, safety can be further increased.

When the predetermined concentration of carbon dioxide of 0.007 (kg/m³) is detected by the concentration detection device 39 that is disposed in the heat medium relay unit 3, it is determined that refrigerant leakage has occurred, and the switch of the concentration detection device 39 is turned OFF and energization of the first shut off device 37 and the second shut off device 38 are stopped. As a result, the first shut off device 37 and the second shut off device 38 are turned into a closed state, and the refrigerant flowing from the outdoor unit 1 through the refrigerant piping 4 can be shut off, and, thus, refrigerant leakage into the indoor space can be prevented.

Note that although in Embodiment 2, an exemplary case is shown in which the concentration detection device 39 is provided in the heat medium relay unit 3, the installing position is not limited to this position. For example, the concentration detection device 39 may be provided in the space in which the heat medium relay unit 3 is disposed rather than in the heat medium relay unit 3. That is, since the aim of disposing the concentration detection device 39 is to detect the refrigerant concentration in the space where people exist, the concentration detection device 39 may be disposed in any position in the space where the heat medium relay unit 3 is disposed. Further, the concentration detection device 39 may be incorporated in a remote control (not shown), for example.

Refrigerant Piping 4

As described above, the air-conditioning apparatus 101 according to Embodiment 2 has several operation modes. In these operation modes, the heat source side refrigerant flows through the refrigerant pipings 4 connecting the outdoor unit 1 and the heat medium relay unit 3.

Piping 5

In some operation modes carried out by the air-conditioning apparatus 101 according to Embodiment 2, the heat medium, such as water or antifreeze, flows through the pipings 5 connecting the heat medium relay unit 3 and the indoor units 2.

Heat Source Side Refrigerant

Although an explanatory case in which carbon dioxide (CO₂) that is known as having a relatively low global warming potential is used as the heat source side refrigerant, other single mixed refrigerants or mixed refrigerants that transmits to a supercritical state may be used as the heat source side refrigerant. For example, a mixture of carbon dioxide and diethyl ether may be used as the heat source side refrigerant.

Heat Medium

As regards the heat medium, for example, brine (antifreeze), water, a mixed solution of brine and water, or a mixed solution of water and an additive with high anticorrosive effect can be used. In the air-conditioning apparatus 101, therefore, even if the heat medium leaks into the indoor space 7 through the indoor unit 2, because the heat medium used is highly safe, contribution to improvement of safety can be made.

The air-conditioning apparatus 101 that employs the above-described configuration is capable of detecting refrigerant leakage from the refrigerant circuit (refrigerant circuit A) and is one with substantially improved safety. Further, since the air-conditioning apparatus 101 uses a refrigerant that transmits to a supercritical state, environmental load can be made small.

In the air-conditioning apparatus 101 according to Embodiment 2, the pressure in the bypass piping 4 d differs depending on the switching state of the first refrigerant flow switching device 11, and the bypass piping 4 d is filled with either a high-pressure refrigerant or a low-pressure refrigerant.

Further, in the cooling main operation mode or the heating main operation mode, when the state (heating or cooling) of the heat exchanger related to heat medium 15 b and the heat exchanger related to heat medium 15 a changes, the water that had been hot is cooled turning into cold water and the water that had been cold is heated turning into hot water, and thus waste of energy occurs. Hence, the air-conditioning apparatus 101 is configured such that during both cooling main operation mode and heating main operation mode, the heat exchanger related to heat medium 15 b is always on the heating side and the heat exchanger related to heat medium 15 a is always on the cooling side.

Furthermore, in the case in which the heating load and the cooling load simultaneously occur in the use side heat exchangers 26, the first heat medium flow switching device 22 and the second heat medium flow switching device 23 corresponding to the use side heat exchanger 26 which performs the heating operation are switched to the passage connected to the heat exchanger related to heat medium 15 b for heating, and the first heat medium flow switching device 22 and the second heat medium flow switching device 23 corresponding to the use side heat exchanger 26 which performs the cooling operation are switched to the passage connected to the heat exchanger related to heat medium 15 a for cooling, so that the heating operation or cooling operation can be freely performed in each indoor unit 2.

Furthermore, each of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23 described in Embodiment 2 may be any of the sort as long as they can switch passages, for example, a three-way valve capable of switching between three passages or a combination of two on-off valves and the like switching between two passages. Alternatively, components such as a stepping-motor-driven mixing valve capable of changing flow rates of three passages or electronic expansion valves capable of changing flow rates of two passages used in combination may be used as each of the first heat medium flow switching devices 22 and the second heat medium flow switching devices 23. In this case, water hammer caused when a passage is suddenly opened or closed can be prevented. Furthermore, while Embodiment 2 has been described with respect to the case in which the heat medium flow control devices 25 each include a two-way valve, each of the heat medium flow control devices 25 may include a control valve having three passages and the valve may be disposed with a bypass pipe that bypasses the corresponding use side heat exchanger 26.

Furthermore, as regards each of the heat medium flow control device 25, a stepping-motor-driven type that is capable of controlling a flow rate in the passage is preferably used. Alternatively, a two-way valve or a three-way valve whose one end is closed may be used. Alternatively, as regards each of the heat medium flow control device 25, a component, such as an on-off valve, which is capable of opening or closing a two-way passage, may be used while ON and OFF operations are repeated to control an average flow rate.

Furthermore, while each second refrigerant flow switching device 18 has been described as if it is a four-way valve, the device is not limited to this type. The device may be configured such that the refrigerant flows in the same manner using a plurality of two-way flow switching valves or three-way flow switching valves. Additionally, a four-way valve may be used to constitute each second refrigerant flow switching device 18.

While the air-conditioning apparatus 101 according to Embodiment 2 has been described with respect to the case in which the apparatus can perform the cooling and heating mixed operation, the apparatus is not limited to the case. Even with an apparatus that is configured with a single heat exchanger related to heat medium 15 and a single expansion device 16 that are connected to a plurality of parallel use side heat exchangers 26 and heat medium flow control devices 25, and is capable of carrying out only a cooling operation or a heating operation, the same advantages can be obtained.

In addition, it is needless to say that the same holds true for the case in which only a single use side heat exchanger 26 and a single heat medium flow control device 25 are connected. Moreover, it is needless to say that no problem will arise even if the heat exchanger related to heat medium 15 and the expansion device 16 acting in the same manner are arranged in plural numbers. Furthermore, while the case in which the heat medium flow control devices 25 are equipped in the heat medium relay unit 3 has been described, the arrangement is not limited to this case. Each heat medium flow control device 25 may be disposed in the indoor unit 2. The heat medium relay unit 3 and the indoor unit 2 may be constituted in different housings.

Typically, a heat source side heat exchanger 12 and a use side heat exchanger 26 are provided with an air-sending device in which a current of air often facilitates condensation or evaporation. The structure is not limited to this case. For example, a heat exchanger, such as a panel heater, using radiation can be used as the use side heat exchanger 26 and a water-cooled heat exchanger which transfers heat using water or antifreeze can be used as the heat source side heat exchanger 12. In other words, as long as the heat exchanger is configured to be capable of transferring heat or removing heat, any type of heat exchanger can be used as each of the heat source side heat exchanger 12 and the use side heat exchanger 26.

Embodiment 2 has been described in which the number of the use side heat exchanger 26 is four. As a matter of course, the number is not limited to this case. Furthermore, Description has been made illustrating a case in which there are two heat exchangers related to heat medium 15, namely, heat exchanger related to heat medium 15 a and heat exchanger related to heat medium 15 b. As a matter of course, the arrangement is not limited to this case, and as long as it is configured so that cooling and/or heating of the heat medium can be carried out, the number may be any number. Furthermore, each of the number of pumps 21 a and that of pumps 21 b is not limited to one. A plurality of pumps having a small capacity may be connected in parallel.

Embodiment 2 has been described with respect to the case in which a single first heat medium flow switching device 22, a single second heat medium flow switching device 23, and a single heat medium flow control device 25 are connected to each use side heat exchanger 26. The arrangement is not limited to this case. A plurality of devices 22, a plurality of devices 23, and a plurality of devices 25 may be connected to each use side heat exchanger 26. In this case, the first heat medium flow switching devices, the second heat medium flow switching devices, and the heat medium flow control devices connected to the same use side heat exchanger 26 may be operated in the same manner.

The above-described air-conditioning apparatuses according to Embodiments 1 and 2 are capable of detecting refrigerant leakage from the refrigerant circuit and are ones with substantially improved safety. Note that the configuration described in Embodiment 1 can be appropriately applied to the configuration of Embodiment 2, and the configuration described in Embodiment 2 can be appropriately applied to the configuration of Embodiment 1.

Reference Signs List

1 outdoor unit; 2 indoor unit; 2 a indoor unit; 2 b indoor unit; 2 c indoor unit; 2 d indoor unit; 3 heat medium relay unit; 4 refrigerant piping; 4 d bypass piping; 5 piping; 6 outdoor space; 7 indoor space; 8 space; 9 structure; 10 compressor; 11 first refrigerant flow switching device; 12 heat source side heat exchanger; 15 heat exchanger related to heat medium; 15 a heat exchanger related to heat medium; 15 b heat exchanger related to heat medium; 16 expansion device; 16 a expansion device; 16 b expansion device; 17 on-off device; 18 second refrigerant flow switching device; 18 a second refrigerant flow switching device; 18 a(1) second refrigerant flow switching device; 18 a(2) second refrigerant flow switching device; 18 b second refrigerant flow switching device; 18 b(1) second refrigerant flow switching device; 18 b(2) second refrigerant flow switching device; 19 accumulator; 21 pump; 21 a pump; 21 b pump; 22 first heat medium flow switching device; 22 a first heat medium flow switching device; 22 b first heat medium flow switching device; 22 c first heat medium flow switching device; 22 d first heat medium flow switching device; 23 second heat medium flow switching device; 23 a second heat medium flow switching device; 23 b second heat medium flow switching device; 23 c second heat medium flow switching device; 23 d second heat medium flow switching device; 25 heat medium flow control device; 25 a heat medium flow control device; 25 b heat medium flow control device; 25 c heat medium flow control device; 25 d heat medium flow control device; 26 use side heat exchanger; 26 a use side heat exchanger; 26 b use side heat exchanger; 26 c use side heat exchanger; 26 d use side heat exchanger; 31 first temperature sensor; 31 a first temperature sensor; 31 b first temperature sensor; 34 second temperature sensor; 34 a second temperature sensor; 34 b second temperature sensor; 34 c second temperature sensor; 34 d second temperature sensor; 35 third temperature sensor; 35 a third temperature sensor; 35 b third temperature sensor; 35 c third temperature sensor; 35 d third temperature sensor; 36 pressure sensor; 37 first shut off device; 38 second shut off device; 39 concentration detection device; 100 air-conditioning apparatus; 101 air-conditioning apparatus; 200 outdoor unit; 201 compressor; 202 oil separator; 203 flow switching device; 204 heat source side heat exchanger; 205 accumulator; 206 oil return capillary; 300 indoor unit; 300 a indoor unit; 300 b indoor unit; 300 c indoor unit; 300 d indoor unit; 301 use side heat exchanger; 301 a use side heat exchanger; 301 b use side heat exchanger; 301 c use side heat exchanger; 301 d use side heat exchanger; 302 expansion device; 302 a expansion device; 302 b expansion device; 302 c expansion device; 302 d expansion device; 303 first shut off device; 303 a first shut off device; 303 b first shut off device; 303 c first shut off device; 303 d first shut off device; 304 second shut off device; 304 a second shut off device; 304 b second shut off device; 304 c second shut off device; 304 d second shut off device; 305 concentration detection device; 306 temperature sensor; 307 temperature sensor; 308 pressure sensor; 400 piping; 400 a piping; 400 b piping; A refrigerant circuit; B heat medium circuit. 

1. An air-conditioning apparatus, comprising: an outdoor unit including at least a compressor and a heat source side heat exchanger; an indoor unit including at least an expansion device and a use side heat exchanger; a refrigerant circuit being formed by refrigerant piping connecting the compressor, the heat source side heat exchanger, the expansion device, and the use side heat exchanger, the refrigerant circuit in which a heat source side refrigerant that transmits to in a supercritical state circulates; a concentration detection device detecting a concentration of the refrigerant that has leaked from the refrigerant circuit, the concentration detection device being provided in the indoor unit or in the installation space of the indoor unit; a shut off device that shuts off the circulation of the heat source side refrigerant on the basis of information from the concentration detection device, the shut off device being provided on both sides of refrigerant outlet and inlet in the indoor unit; and the shut off device makes an electrical component thereof driven by DC power supply, is in an opened state when energized, and is in a closed state when not energized.
 2. An air-conditioning apparatus, comprising: an outdoor unit including at least a compressor and a heat source side heat exchanger; a heat medium relay unit including at least a heat exchanger related to heat medium, an expansion device, and a pump; an indoor unit including at least a use side heat exchanger; a refrigerant circuit being formed by refrigerant piping serially connecting the compressor, the heat source side heat exchanger, the expansion device, and a refrigerant side passage of the heat exchanger related to heat medium, the refrigerant circuit in which a heat source side refrigerant that transmits to a supercritical state circulates; a heat medium circuit being formed by piping serially connecting a heat medium side passage of the heat exchanger related to heat medium, the pump, and the use side heat exchanger, the heat medium circuit in which a heat medium circulates; a concentration detection device detecting a concentration of the refrigerant that has leaked from the refrigerant circuit, the concentration detection device being provided in the heat medium relay unit or in the installation space of the heat medium relay unit; a shut off device that shuts off the circulation of the heat source side refrigerant on the basis of information from the concentration detection device, the shut off device being provided on both sides of refrigerant outlet and inlet in the heat medium relay; and the shut off device makes an electrical component thereof driven by DC power supply, is in an opened state when energized, and is in a closed state when not energized.
 3. (canceled)
 4. The air-conditioning apparatus of claim 1, wherein the energization of the shut off device is turned off when the concentration of the heat source side refrigerant that is detected by the concentration detection device is at or more than a predetermined concentration.
 5. The air-conditioning apparatus of claim 4, wherein the predetermined concentration is set under a practical limit of leakage.
 6. (canceled)
 7. The air-conditioning apparatus of claim 1, wherein the shut off device includes a stepping motor as the electrical component.
 8. The air-conditioning apparatus of claim 1, wherein an amount of leakage of the heat source side refrigerant from the shut off device is 3.0×10⁻⁹ (m³/sec) or less.
 9. The air-conditioning apparatus of claim 1, wherein during cooling operation the CV value of the shut off device disposed on the high-pressure side is 1 or more and the CV value of the shut off device disposed on the low-pressure side is 5 or more.
 10. The air-conditioning apparatus of claim 1, wherein a minimum operating pressure differential of the shut off device is at around 0 (kgf/cm²).
 11. The air-conditioning apparatus of claim 1, wherein the shut off device is capable of passing the heat source side refrigerant in both directions.
 12. The air-conditioning apparatus of claim 1, wherein an electric power supply to the concentration detection device is from a commercial power supply or from a battery. 